1. Field of the Invention
The present invention relates to a brine composition for a frozen food, which is used for a brine freezing method for foods, and also relates to a method for producing a frozen food.
2. Description of the Related Art
Both at home and abroad, freezing food is an inevitable topic that needs to be addressed regarding requirements such as the beneficial use of foods upon surplus harvest and bumper catch, adaptation to diversification of dietary habits, and inclination to safe and reliable foods free of additives in addition to the fact that more elaborate and delicious frozen foods are desired.
In order to provide consumers with delicious frozen foods, the following three requirements must be satisfied: acquisition of fresh materials, freezing and thawing techniques to maintain the deliciousness of foods before freezing, and processing techniques suitable for freezing and thawing. In addition, infrastructure development for the distribution of frozen foods is also essential.
Food freezing methods are classified into air blast systems, contact freezing systems, brine systems, liquid nitrogen or liquid carbon dioxide gas freezing systems, and the like depending on the cooling medium used.
Among them, a method of contacting foods with cold air in a freezer (air blast system) is well known. However, the cold air flow hardly contacts the foods sufficiently and that tends to cause uneven freezing on the back, side, and bottom surfaces of the foods placed in the freezer. In addition, due to low heat conductivity, the time for the foods to be frozen to pass through the maximum ice crystal generation zone (−1 to −5° C.) is long so that water in the tissues (cells) of the foods becomes ice crystals which grow and cause tissue breakdown, thereby resulting in the main cause of quality degradation due to dripping at the time of thawing.
Accordingly, in order to prevent quality degradation of foods due to freezing, it is important to pass the foods through the maximum ice crystal generation zone in a short time.
The brine system has as high as about 20 times the heat conductivity compared to the air blast system (Table 1) and is favorable when high quality foods are produced by rapid freezing. However, currently, when most frozen foods are unwrapped, the air blast system is predominant.
TABLE 1Coefficient of heat conductivity (W/m2 · K) of mediumcoefficient ofmediumheat conductivityconditioninactional air4.5~8  air in air blast (I)12~23air flow velocity 1.5~2 m/sair in air blast (II)23~35air flow velocity 4~5 m/sbrine freezing400~500flow liquidin contact freezing device 30~100metal
Meanwhile, there exists a desire for higher quality frozen foods, and a refrigerator has been developed which provides higher heat conductivity due to the application of a high-voltage electric field of 5 to 50 kV and an alcohol brine freezing which is capable of rapidly freezing in an extremely short time and also has low running costs (Japanese Patent No. 3639499 (Patent Document 1) and Japanese Laid-Open Publication No. 8-126465 (Patent Document 2)).
However, these conventional methods have the following problems.
When an alcohol is used as the cooling medium, the medium absorbs water from the air and reduces the alcohol content thereof, and therefore, the temperature is hardly reduced. Accordingly, the freezing temperature is also high. For example, when ethanol is used as the brine, although ethanol is safe for foods, low in viscosity and consequently useful as a cooling medium for the brine system, there is a problem that when an aqueous ethanol solution is cooled to −35° C. or lower, the solution adsorbs water in the air during operation, reducing the ethanol content, thereby raising the freezing temperature.    [Patent Document 1] Japanese Patent No. 3639499    [Patent Document 2] Japanese Laid-Open Publication No. 8-126465